drivers: gpio: nrfx: ensure ch variable stays allocated during use
drivers: gpio: nrfx: ensure ch variable stays allocated during use

Inside gpio_nrfx_pin_interrupt_configure, the "ch" variable is allocated
inside the "if", but then it gets dereferenced and the pointer saved in
trigger_config, which is used in the outer context.

This works fine right now, but that memory location could possibly be
reused by another automatic variable if the code gets changed.

Moving it in the function context to avoid any potential problem.

Signed-off-by: Fabio Baltieri <161d407f4dc681bfd4aedb33b8273b2aafd727bc@gmail.com>

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